题目

如图，Rt△AB′C′是Rt△ABC以点A为中心逆时针旋转90°而得到的，其中AB＝1，BC＝2，则旋转过程中弧CC′的长为( ) A.π           B.π          C．5π            D.π 答案：.A---What did you do during your summer holiday?---I spent my holiday ______ English in summer classesA.improvingB.improvesC.to improve